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Using the Model PB3 for RF Bias Applications

RF_Bias_generator_rotating_substrate_holder The Series PB3 integrated RF power system is the perfect choice to power small substrate stages and bias-able electrodes in a plasma system. Manitou has supplied 100’s of the Model PB3-100D RF systems (see a typical unit on the right side of the image) to OEMs and end-users to provide finely controlled 13.56MHz bias plasma power.




Why should you consider using the Model PB3 in your plasma system ?

  • Integrated design including the RF generator + the impedance matching network.
  • Single, compact enclosure
  • Easy to interface: three (3) connections including AC Mains, control-metering and “plasma”.
  • Quick set-up: select and connect the proper series inductor tap.

How does the PB3 integrated system compare to using a traditional 2-piece (separate RF generator and match) component set ?

  • No additional interconnects required
  • Lower cost and complexity
  • The Model PB3 offers analog and contact closure control.
  • The Model PB3 includes a manually adjusted (front panel) impedance matching controls.
  • Space saving at the vacuum process chamber (a single coax cable connects the pB3 to the substrate stage connector)

What are the advantages and disadvantages of manually adjusted matching network tuning ?

  • When the PB3 is used to power small to medium size substrate stages & platforms, the plasma discharge is typically stable, well behaved as well as presenting a constant impedance load. This means that the matching network settings will not need to be adjusted often.
  • When multiple plasma process recipes are run, there may be slight changes to the plasma impedance resulting in different levels of reflected power. These variations are small and the user can choose to fine tune the match or if the reflected power is below 10% (of the forward power) do nothing at all. As RF power is applied to the substrate to ultimately create a DC “self” bias voltage, these reflected power variations do not typically result in much variation of the self bias.

What type and length of coaxial cable is used to connect the PB3 to the substrate stage ?

  • When using 100 watts or less, we recommend type RG303 or RG400
  • When using up to 300 watts of power, we recommend type RG393
  • The length “rule of thumb” is: shorter is better !   We have customers that successfully use up to 15 feet (4.6M) of cable. It should be noted that there will be some power loss with longer cable lengths. Small diameter (1>3″) substrate stages typically require under 50 watts of RF power so, the PB3-100 (rated at 100 watts) will provide sufficient power headroom to overcome the losses – and maintain the DC self bias level. Larger diameter stages may require more than 100 watts with the same headroom considerations  to apply.
  • Manitou also recommends dressing the “plasma” cable at least 4″ away from other control and electrical wiring inside the cabinet as there may be some “common mode” RF radiation along the outside of the cables shield. If this is a problem, we suggest that a cable with a Faraday shield be used as this cable type will choke off or attenuate any common mode RF current. Manitou can supply these and other cables – premade  and ready to install.